Impact of breast cancer grade discordance on prediction of outcome
Institution: School of Medicine, University of Nottingham; Faculty of Medicine, Menoufia University
Corresponding Researcher: Emad Rakha
Data Link(s): NA
Keyword(s): agreement, breast pathology, discordance, grade, outcome
Summary
AIMS. Histological grade is an independent prognostic variable in breast cancer (BC). Previous concordance studies of BC grade have reported moderate levels of agreement; a typical finding in morphological assessment of biological variables. This study aimed to investigate the impact of discordance on the prognostic value of grade and to identify the best reporting approach in borderline cases. METHODS AND RESULTS. A large (n = 1675) well-characterised annotated cohort of BC, originally graded in routine practice using glass slides, was re-graded twice by an expert breast pathologist using virtual microscopy with a 3-month washout period. Outcome was assessed using breast cancer-specific and distant metastasis-free survival (median follow-up = 135 months). Fifty-eight per cent of the cases showed absolute agreement in the three separate grading sessions, whereas grades 1/2 and 2/3 discordance were observed in 21% and 21%, respectively. Absolute intra-observer agreement using virtual microscopy was observed in 77% of the cases, whereas 13% and 10% showed grades 1/2 and 2/3 discordance, respectively. Despite the concordance, outcome analysis revealed significant associations between tumour grade and patients' outcome in the three grading sessions. Grades 1/2 and 2/3 discordant cases showed intermediate survival between grades 1 and 2 tumours and grades 2 and 3 tumours, respectively. Grades 1/2 discordant cases showed a worse outcome when compared with grade 1 tumours (P = 0.008) but no statistical difference was identified when compared with grade 2 tumours. Similarly, grades 2/3 discordant cases showed a significant difference from grade 2 tumours (P < 0.001), but no statistical difference was identified when compared with grade 3 tumours. CONCLUSIONS. Breast cancer grade discordance is probably a reflection of biologically, and hence morphologically, borderline tumours. Cases with borderline features for grade are more likely to behave similarly to the higher-grade category. Repeating histological grade of borderline cases or double reporting may improve correlation with outcome.
